1. Field of the Invention
The present invention relates to an enclosed switchgear in which a vacuum valve provided with a pair of switching contacts and a moving mechanism part for moving the vacuum valve are disposed in a gas tank filled with an insulating gas.
2. Description of the Related Art
Hitherto, electric wiring has been connected and disconnected by a vacuum circuit breaker (as disclosed in, for example, the Japanese Patent Publication (unexamined) No. 1997-147700 (pages 1 to 5, FIGS. 1 to 7)). In this conventional vacuum circuit breaker disclosed in the Japanese Patent Publication (unexamined) No. 1997-147700, all members such as vacuum valve, insulating rod, contact pressure adjusting spring are left open to the atmospheric air.
However, in such a case the all the members are left open (exposed) to the air, in order to secure a predetermined dielectric breakdown voltage, the entire switchgear becomes unavoidably large in size, and humidity in the air and foreign matter contained in the air often stick to the surface of the insulating rod. As a result, such a trouble as malfunction is caused by decrease in insulation resistance of the surface of the insulating rod.
To cope with such a trouble, it may be an idea that the entire enclosed type switchgear is miniaturized by disposing a set of electric circuit parts, which is one of the members forming the conventional vacuum circuit breaker, in a gas tank and effectively preventing decrease in insulation resistance of the insulating rod surface. When installing the mentioned conventional vacuum circuit breaker with its form unchanged in a gas tank, enclosed type switchgear of a construction as shown in FIG. 7 can be obtained.
Referring to FIG. 7, reference numeral 1 is a gas tank filled with insulating gas, and numeral 2 is a vacuum valve disposed in the gas tank 1 and fixed by a member not shown. The vacuum valve 2 is provided with a stationary switching contact 4 and a moving switching contact 5 forming a pair in a housing 3 thereof. Numeral 8 is a stationary current-carrying shaft integrally provided with the stationary contact 4 of the vacuum valve 2, numeral 9 is a moving current-carrying shaft integrally provided with the moving contact 5 of the vacuum valve 2, and both of the current-carrying shafts 8 and 9 extend through and protrude out of the housing 3. A wiring of a main circuit not shown is connected to the stationary current-carrying shaft 8, and another wiring of a main circuit not shown is connected to the moving current-carrying shaft 9 through a flexible conductor 10.
Numeral 11 is an insulating rod fixed on the other end side of the moving current-carrying shaft 9. This insulating rod 11 transmits operation force from an operation mechanism part 18 described later to the moving contact 5 of the vacuum valve 2 and electrically insulates between the moving current-carrying shaft 9 and a contact pressure adjusting spring 19.
Numeral 14 is an arc shield covering the pair of contacts 4, 5, and numeral 15 is a guide part formed on the housing 3 so that the moving current-carrying shaft 9 extends through and is supported by the guide part 15. Numeral 16 is a bellows for keeping airtightness in the vacuum valve 2.
Numeral 17 is an operating rod disposed so as to extend through a guide part 20 formed on the gas tank 1, and numeral 18 is the operation mechanism part provided on the operating rod 17 outside the gas tank 1. Numeral 19 is the contact pressure adjusting spring disposed on the operating rod 17 inside the gas tank 1. This contact pressure adjusting spring 19 presses the contact 5 on the contact 4 with appropriate pressure to bring the contacts 4, 5 of the vacuum valve 2 into a closed electrode state. This contact pressure adjusting spring 19 is joined to the mentioned insulating rod 11.
It is to be noted that, in the case of constituting the enclosed type switchgear by disposing the conventional vacuum circuit breaker with its form unchanged in the gas tank 1, the insulating rod 11 is directly fixed to the moving current-carrying shaft 9. Further, in this constitution, the contact pressure adjusting spring 19 is mounted on the operating rod 17 and the mentioned spring 19 is joined to the insulating rod 11. As a result, the mentioned moving current-carrying shaft 9, including the vacuum valve 2 and the stationary current-carrying shaft 8, is kept at a state of being applied with a high-voltage. Meanwhile, the contact pressure adjusting spring 19 is insulated by the insulating rod 11 and is therefore kept at ground potential, including the operating rod 17, the operation mechanism part 18, and the gas tank 1 wall face.
In the mentioned construction, when the contacts 4, 5 of the vacuum valve 2 are in an opened electrode state and the operation mechanism part 18 is operated from this state to drive the operating rod 17 rightward in the drawing, driving force is transmitted to the moving current-carrying shaft 9 through the contact pressure adjusting spring 19 and the insulating rod 11. As a result, the contacts 4, 5 of the vacuum valve 2 are brought into the closed electrode. Therefore, an electric current flows through the main circuit through, for example, the stationary current-carrying shaft 8, the contacts 4, 5 of the vacuum valve 2, the moving current-carrying shaft 9, and the flexible conductor 10. On the other hand, when the operation mechanism part 18 is operated to drive the operating rod 17 leftward in the drawing, the contacts 4, 5 of the vacuum valve 2 are brought into the opened electrode, thus the electric current flowing through the main circuit being interrupted.
However, the enclosed type switchgear constructed by disposing the conventional vacuum circuit breaker with its form unchanged in the gas tank 1 as shown in FIG. 7 has the following problems.
That is, one end of the operating rod 17 is supported on the operation mechanism part 18, and the other end of the operating rod 17 is supported on the guide part 20 of the gas tank 1, therefore the operating rod 17 supported at such two points hardly oscillates vertically along the direction perpendicular to the shaft direction.
On the other hand, the moving current-carrying shaft 9 is supported only at the middle thereof by the guide part 15 formed on the housing 3 of the vacuum valve 2, and the moving contact 5 faces the stationary contact 4 on one end side of the moving current-carrying shaft 9, and the other end of the moving current-carrying shaft 9 is joined to the flexible contact pressure adjusting spring 19 through the insulating rod 11. Owing to such a structure, the members from the insulating rod 11 through the moving current-carrying shaft 9 to the moving contact 5 as a whole are easy to oscillate along the direction perpendicular to the shaft direction with the guide part 15 of the vacuum valve 2 acting as the supporting point. As a length L2 from the insulating rod 11 to the moving contact 5 is longer, the members as a whole oscillate more.
As described above, in the case that oscillation amount of the members from the insulating rod 11 through the moving current-carrying shaft 9 to the moving contact 5 is large as a whole, there is an increase in offset load on the surface of the contacts 4, 5 of the vacuum valve 2 and an increase in friction force on the guide part 15 on which the moving current-carrying shaft 9 is supported. The increase in the offset load causes an increase in contact resistance on the surface of the contacts 4, 5 of the vacuum valve 2, eventually resulting in a power loss. Moreover, when increasing the friction force on the guide part 15, more operation force is required for the operation mechanism part 18, which obstructs smooth operation.
If the moving current-carrying shaft 9 is shortened in length, the length L2 from the insulating rod 11 to the moving contact 5 is also shortened, and it is possible to decrease the oscillation amount. However, in actual construction, it is necessary to attach the flexible conductor 10 and various members not shown in the middle of the moving current-carrying shaft 9. While securing a space for these members, achieving a large reduction in length of the moving current-carrying shaft 9 is not always easy, thus there is a limit in the shortening.